Amicus Curiae Brief presented by ClientEarth 21 November 2016 55. The treaty does not specify a particular concentration of greenhouse gasses, nor does it define what exactly is meant by dangerous anthropogenic interference in the climate system. 56. In 2012, the parties to the UNFCCC formally adopted the target of limiting greenhouse gas concentrations such that the global average temperature would rise no more than 2 degrees above pre-industrial levels.44 Scientists have noted that the 2 degree target was a political consensus formulated after an analysis of the trade off between expense and risks, and does not necessarily reflect a 'safe' upper limit under which no harmful effects will occur.45 5.2 The Paris Agreement 57. The Paris Agreement was agreed in December 2015 at the 21st Conference of the Parties to the UNFCCC. It entered into force on Friday, 4 November 2016.46 This means that the agreement is now operational and has legal force under international law. The Paris Agreement commits countries to the submission and implementation47 of nationally determined emissions reduction targets (known as NDCs), in order to achieve the overall objective of limiting temperature rise to well-below 2 degrees below pre-industrial levels. 58. The core objective of the Agreement is contained in Article 2 which states that the parties aim to: 44 Report of the Conference of the Parties on its Eighteenth Session, Held in Doha from 26 November to 8 December 2012 - Addendum - Part Two: Action Taken by the Conference of the Parties at its Eighteenth Session FCCC/CP/2012/8/Add.1 (UNFCCC, 2012). 45 Knutti et al, 'A scientific critique of the two-degree climate change target' Nature Geoscience 9, 13–18 (2016). 46 UNFCCC, The Paris Agreement, http://unfccc.int/paris_agreement/items/9485.php 47 Arguably implied under Article 4(2). 31